
#include<stdio.h>
#include<unistd.h>
#include<semaphore.h>
#include<pthread.h>
#include<signal.h>



  sem_t sem;

void callback(int sig){
  sem_post(&sem);

}

int main(){
  signal(2,callback);
  sem_init(&sem,0,1);

  sem_wait(&sem);
  sem_wait(&sem);
  printf("If the code can run here,then hell . \n ");
  return 0;
}
